What's this noise?
 

I just got my car back from an engine rebuild and now there's a strange clutch related noise. The guys said that if it doesn't go away in a few days to bring it back and they'll take a look, but in the meantime I'm really curious to know what it could be.

So the noise is a kind of chattery/knocking/grinding noise and it happens when I'm letting the clutch back up, i.e. when taking off from stationary (forward or reverse) or changing down a gear. It's only barely audible on take-off, but when changing down it's really loud and horrible as the engine brakes. It's not noticeable when changing up gears and it doesn't happen when stationary (clutch depressed or not).

Here's a couple of videos. Sound quality isn't great but if you turn it up loud with earphones then the noise can be heard.

https://photos.app.goo.gl/CHojva7iK8DmXiEd2

https://photos.app.goo.gl/TGGptE45VbPaByg12

So just for the record; one of the needles in the pilot bearing got knocked out by the shaft when the engine and box were being put back together. Replaced and everything is perfect now.